Fruits and vegetables are living organisms that continue essential chemical and physiological activities after harvest. These activities can include physiological breakdown, physical injury to tissue, invasion by microorganisms, and moisture loss. Additionally, some fruits and vegetables can suffer damage while being transported hot from the field. Thus, the time between harvest and cooling to remove field heat and slow plant respiration, otherwise known as the “cut-to-cool” interval, is critical for ensuring the quality and safety of the product.
The term “cold chain” refers to the uninterrupted temperature management of perishable product in order to maintain quality and safety from the point of post-harvest cooling through the distribution chain to the final consumer. The cold chain ensures that perishable product are safe and of high quality at the point of consumption. Failing to keep product at the correct temperatures can result in a variety of negative attributes including, among others, textural degradation, discoloring, bruising, and microbial growth.
Typically, fruits and vegetables may be harvested into trucks which carry the produce to fixed-base cooling facilities, where the produce is cooled and the cold chain begins. The produce is then transported from the cooling facilities to their final destination, often in refrigerated semitrailers called reefers. Starting the cold chain at the cooling facility has several drawbacks. For example, during transport from the field to the cooling facility in open vehicles, the produce is generally exposed to wind, sun and heat, which can result in moisture loss, physiological breakdown and textural degradation. A further drawback is the need to have produce grown proximately to cooling facilities to minimize the time between harvest and start of the cold chain.
Pressure cooling units at a cooling facility are generally referred to as fixed-base units, in that it is a difficult and time consuming process to break down and transport these cooling units. First, the fixed-base cooling units tend to be large, and do not break down into small sub-units which may be easily transported. Second, ammonia is a preferred circulating refrigerant within the evaporator/condenser assembly. Ammonia is a highly controlled substance due to its potential dangers if spilled, and Environmental Protection Agency's Risk Management Program (RMP) promulgates several regulations for the use and transport of ammonia. For example, operating and safety permits are required when working with 500 lbs. of ammonia or more (fixed-base cooling units use at least this amount). Moreover, when transporting this quantity of ammonia, the ammonia must first be pumped down and evacuated from the pipes and condenser circulation system, and a specialized and authorized technician must be present to oversee the break down process. All of this makes it difficult, time-intensive and costly to break down fixed-based cooling units.